Fuel supply device for an internal combustion engine and method of supplying varying fuels to an internal combustion engine

The fuel supply system has at least one gas tank (5) for gaseous fuel, at least one liquid gas tank (4) for liquid gas fuel and a mixer (1) connected to a control device (13) with take-off lines (2f, 2g) to the liquid gas tank and the gas tank. On the output side it is has a gas line (3) connected to at least one combustion chamber.